High pressure liquid pump

ABSTRACT

A HIGH PRESSURE PUMP HAS A PUMP CYLINDER CONTAINED BY AN OUTER PRESSURE VESSEL, AN INTERSPACE BEING DEFINED BETWEEN THE PUMP CYLINDER AND THE PRESSURE VESSEL. LIQUID IS PRESSURISED IN THE PUMP CYLINDER BY A PISTON AND PRESSURISED LIQUID IS FED THROUGH A NONRETURN VALVE FROM THE PUMP CYLINDER INTO THE INTERSPACE ON THE PRESSURISING STROKE OF THE PISTON. SUPPLY OF LIQUID BY THE PUMP AT   CONSTANT PRESSURE IS FROM THE INTERSPACE. AN ACCUMULATOR SPACE OF VARIABLE VOLUME MAY BE PROVIDED CONNECTED WITH THE INTERSPACE TO ACCOMMODATE FOR DIFFERENCES BETWEEN THE RATE OF SUPPLY OF LIQUID FROM THE INTERSPACE AND THE RATE OF FEED OF LIQUID FROM THE PUMP CYLINDER INTO THE INTERSPACE.

Jan. 19, 1971 PiGOTT ETAL 3,556,692

I HIGH PRESSURE LIQUID PUMP Filed March 4, 1969 2 Sheets-Sheet 1 Jan.19, 1971 A. E. PIGOTT ETAL HIGH PRESSURE LIQUID PUMP 2 Sheets-Sheet 2Filed March 4, 1969 United States Patent 3,556,692 HIGH PRESSURE LIQUIDPUMP Albert Edward Pigott, Clifton, Preston, and Peter John Thompson,St. Annes-on-Sea, England, assignors to United Kingdom Atomic EnergyAuthority, London, England Filed Mar. 4, 1969, Ser. No. 804,102 Claimspriority, application Great Britain, Mar. 8, 1968, 11,590/68 Int. Cl.F04b 11/00 US. Cl. 417-540 8 Claims ABSTRACT OF THE DISCLOSURE A highpressure pump has a pump cylinder contained by an outer pressure vessel,an interspace being defined between the pump cylinder and the pressurevessel. Liquid is pressurised in the pump cylinder by a piston andpressurised liquid is fed through a nonreturn valve from the pumpcylinder into the interspace on the pressurising stroke of the piston.Supply of liquid by the pump at constant pressure is from theinterspace. An accumulator space of variable volume may be providedconnected with the interspace to accommodate for differences between therate of supply of liquid from the interspace and the rate of feed ofliquid from the pump cylinder into the interspace.

BACKGROUND OF THE INVENTION This invention relates to high pressurefluid pumps and in particular to an improved high pressure fluid pumpcapable of delivering a continuous flow of high pressure fluid at a highflow rate and at a steady feed pressure.

There is an application for such a pump, particularly for the pumping ofliquids, in many fields of high pressure technology, particularapplications being in respect of the isostatic compaction of powders andthe hydrostatic extru! ion process.

In the hydrostatic extrusion process a billet is extruded from a chamberthrough a die by pressurisation of liquid in the chamber about thebillet. Liquid may be pressurised about the billet by a ram acting inthe bore of the extrusion chamber itself, the billet being extruded by asingle stroke of the ram. Unfortunately in this way of carrying out theprocess, instability of the ram by buckling leads to restriction of theram length to diameter ratio which may be used. Hence because of thelimitation imposed on ram length to diameter ratio a limitation isimposed on the length of extrusion chamber which can be employed. Toovercome this ditficulty and enable the use of an extrusion chamber oflarge length to diameter ratio it has been proposed to generate liquidpressure in a separate pump, having a pump cylinder of equal volume tothe volume of liquid required for carrying out extrusion of the billet,but having a length to diameter ratio small enough to avoid bucking ofthe pump piston. In order to achieve this, the diameter of the pumpcylinder is always much larger than that of extrusion container, thusincreasing the cost of the equipment. This difliculty is overcome if therequired volume of high pressure liquid for the extrusion process isdelivered to the extrusion container by a pump having a small cylinderin which the pump piston undergoes several strokes.

A difiiculty arises in use of a pump as described above due to thelimited fatigue life of the pump cylinder which is subjected toalternating high and low internal pressures and hence to a cyclictensile strain variation. Also supply of liquid by the pump isintermittent as feed occurs only on the pumping stroke of the piston.

Pressure cycling in the bore of the extrusion chamber may be avoided byprovision of a hydraulic accumula- 3,556,692. Patented Jan. 19, 1971 torin the feed line from the pump to the extrusion chamber, but the fatiguelife of the pump cylinder remains the limiting factor.

SUMMARY OF THE INVENTION According to the invention a high pressurefluid pump has its cylinder contained by a pressure vessel, aninterspace being defined between the pump cylinder and the pressurevessel, means being provided for controlled feeding of pressurised fluidfrom the pump cylinder into the interspace, supply of pressurized fluidat constant pressure being from the interspace.

The interspace defined between the pump cylinder and the pressure vesselmay be of variable volume to accommodate for differences between therate of feeding of fluid from the pump cylinder into the interspace andthe rate of supply of pressurised fluid from the interspace.

In another arrangement a separate fluid accumulator space of variablevolume is provided connected with the interspace defined between thepump cylinder and the pressure vessel to accommodate for diiferencesbetween the rate of feeding of fluid from the pump cylinder into theinterspace and the rate of supply of pressurised fluid from theinterspace. In this case the fluid accumulator space may be an extensionof the interspace defined between the pump cylinder and the pressurevessel, variation of the volume of the fluid accumulator space beingobtained by longitudinal movement of the pump cylinder and the pressurevessel relative to each other. In a particular arrangement the pumpcylinder may have an axial extension of smaller cross section than themain body of the pump cylinder, the axial extension of the pump cylinderbeing sealed in passage through the wall of the pressure vessel and thefluid accumulator space of variable volume being defined between theaxial extension of the pump cylinder and the pressure vessel, variationof the volume of the fluid accumulator space being obtained bylongitudinal movement of the pump cylinder and the pressure vesselrelative to each other.

The means for controlled feeding of pressurised fluid from the pumpcylinder into the interspace between the pump cylinder and the pressurevessel may be a nonreturn valve. In a particular arrangement the meansfor controlled feeding of pressurised fluid from the pump cylinder intothe interspace between the pump cylinder and the pressure vessel maycomprise a valve seating around one end of the bore of the pumpcylinder, the valve seating bearing against a valve member at the end ofthe pump cylinder, means being provided for establishing a pressurebetween the valve seating and the valve member to control the pressureat which fluid feeds between the valve seating and the valve member fromthe pump cylinder into the interspace. In this arrangement the pumpcylinder may have the feature of an axial extension of smaller crosssection than the main body of the pump cylinder, the axial extension ofthe pump cylinder being sealed in passage through the wall of thepressure vessel, a fluid accumulator space being thus defined betweenthe axial extension of the pump cylinder andthe pressure vessel, thepressure vessel being longitudinally movable relative to the pumpcylinder whereby the fluid accumulator space is of variable volume toaccommodate for differences between the rate of feeding of fluid fromthe pump cylinder into the interspace and the rate of supply ofpressurised fluid from the interspace, means being provided for loadingthe pressure vessel longitudinally to maintain the pressure of the fluidin the accumulator space and in the interspace between the pump cylinderand the pressure vessel, the pressure of the fluid in the accumulatorspace acting on a shoulder between the axial extension of the pumpcylinder and the main body of the pump cylinder to apply a longitudinalloading on the pump cylinder, which establishes the pressure between thevalve seating and the valve member to control the pressure at whichfluid feeds from the pump cylinder into the interspace.

A plunger or piston may be provided in the bore of the pump cylinder forinduction of fluid into and pressurisation of fluid in the pumpcylinder, the means for loading the pressure vessel longitudinally tomaintain the pressure of fluid in the accumulator space and in theinterspace between the pump cylinder and the pressure vessel comprisinga low pressure piston and cylinder arrangement acting on the pressurevessel, the cylinder of the piston and cylinder arrangement having aconnection with the bore of the pump cylinder through a nonreturn valvefor feed of low pressure fluid into the pump cylinder on the inductionstroke of the plunger in the pump cylinder.

The invention is particularly concerned with a high pressure pump inwhich fluid pressure in the pump cylinder varies cyclically duringpumping. This is the case for example where pumping is performed by areciprocating ram or piston operating in the pump cylinder. Normally thepump cylinder would be subjected to a cyclic tensile strain variation.However as the high pressure liquid in the interspace between the pumpcylinder and the pressure vessel acts on the outer surface of the pumpcylinder the pump cylinder will only be subjected to compressive cyclicstrains. The fatigue life of the pump cylinder under this type ofloading will be greater than in the case where the outer surface of thepump cylinder is unsupported and the pump cylinder is subjected to atensile cyclic strain variation. As the pressure of the liquid in theinterspace between the pump cylinder and the pressure vessel is constanttherefore the pressure vessel will not be fatigued.

DESCRIPTION OF THE DRAWINGS An embodiment of the invention will now bedescribed with reference to the accompanying drawings in which: FIG. 1is a centre line section of a high pressure liquid pump according to theinvention.

FIG. 2 is a schematic arrangement of a typical application of the pumpin hydrostatic extrusion apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the construction shown inFIG. 1 of the drawings a high pressure hydraulic pump comprises a bedplate 1 on which there is mounted a pump base 2. The pump base 2comprises a circular plinth 3 having an integral flange 4 and is mountedon the bed plate 1 by bolts 5.

A low pressure cylinder 6 is a sliding fit on the flange 4 of the pumpbase 2, the low pressure cylinder 6 having an annular base 7, which is asliding fit about the plinth 3 of the pump base 2. Sealing between thecylinder 6 and the flange 4 of the pump base 2 is by means of a lowpressure seal 8 whilst sealing between the end wall of the cylinder 6and the plinth 3 of the pump base 2 is by means of a low pressure seal9.

A pump cylinder 10 is mounted on the pump base 2. The pump cylinder 10has a longitudinal bore 11 with a counterbore 12 at its lower end whichfits about an upstanding valve member 13 on the pump base 2. Thecounterbore 12 has a flat seating 14, which seats on the upper end faceof the valve member 13. The flat seating 14 of the counterbore 12 andthe upper end face 15 of the valve member 13 have hard metal facings 16and 17 respectively. The upper end of the valve member 13 is of reduceddiameter so defining an annular space 18 in the counterbore 12 of thepump cylinder 10. The valve member 13 is sealed in the counterbore 12 bya mitre ring and O-ring seal 19. An outer pressure vessel 20 is fittedabout the pump cylinder 10 and is clamped end to end with the lowpressure cylinder 6 by bolts 21. The cojoined cylinder 6 and the outerpressure vessel 20 slide vertically on guide pillars 22 which arescrewed into the bed plate 1, the upper ends of the pillars 22 beingscrewed into a fixed support ring 23. The low pressure cylinder 6 isfitted in a support flange 24 having guide bushes 25 which are a slidingfit on the guide pillars 22. The outer pressure vessel 20 is fitted witha support flange 26 having guide bushes 27 which are also a sliding fiton the guide pillars 22.

An annular interspace 28 is defined between the bore 29 of the outerpressure vessel 20 and the pump cylinder 10. A mitre ring O-ring seal 30seals between the lower end of the bore 29 of the outer pressure vessel20 and the outer surface of the pump cylinder 10.

The pump cylinder 10 has an upper extension 31 of smalled externaldiameter than the main body of the pump cylinder 10. An annular plug 32is screwed into the upper end of the bore 29 in the outer pressurevessel 20. A sealing ring 33 seals between the bore 29 of the outerpressure vessel 20 and the extension 31 of the pump cylinder 10 belowthe plug 32. A pressurised oil accumulator space 34 is defined in theupper end of the bore 29 of the vessel 20 surrounding the upperextension 31 of the pump cylinder 10.

A liquid pressurising ram 35 is entered into the bore 11 of the pumpcylinder 10. The ram 35 is sealed in the bore 11 of the pump cylinder 10by a mitre ring and O- ring seal 36.

An oil inlet port 37 for inlet of a feed of low pressure oil into thepump is provided in the plinth 3 of the pump base 2. The inlet port 37is connected with the low pressure cylinder 6 by a cross drilling 38 inthe pump base 2. A second cross drilling 39 in the pump base 2 connectswith a low pressure oil inlet port 40 in the valve member 13 of the pumpbase 2. The inlet of oil from the port 40 into the bore 11 of the pumpcylinder 10 is controlled by means of a high pressure nonreturn valve 41fitted in the valve member 13. A low pressure oil feed line 42 isconnected with the oil inlet port 37 by a threaded union nut 43. A highpressure oil delivery port 44 in the valve member 13 of the pump base 2leads from the annular space 18 defined in the counterbore 12 of thepump cylinder surrounding the upper end of the valve member 13. A crossdrilling 45 in the pump cylinder 10 connects the annular space 18 withthe annular interspace 28 defined between the bore 29 of the outerpressure vessel 20 and the pump cylinder 10. A high pressure oil out letline 46 is connected with the high pressure oil delivery port 44 by athreaded union nut 47.

In operation of the pump described above low pressure oil is suppliedfrom the oil feed line 42 to the oil inlet port 37 and the low pressurecylinder 6 (via the cross drilling 38). During the upward inductionstroke of the ram 35 in the bore 11 of the pump cylinder 10, lowpressure oil enters the bore 11 from the low pressure cylinder 6 via thecross drilling 39 and the oil inlet port 40 through the open highpressure nonreturn valve 41. The downward pressurising stroke of the ram35 closes the high pressure nonreturn valve 41 and increases the oilpressure in the bore 11 of the pump cylinder 10 until a pressure isachieved which forces oil to pass under pressure from the bore 11 of thepump cylinder 10 between the end face 15 of the valve member 13 and theflat seating 14 of the counterbore 12 in the pump cylinder 10. Thepressurised oil enters the annular space 18 in the counterbore 12 andfrom the annular space 18 the pressurised oil passes through the crossdrilling 45 into the interspace 28 defined between the outer pressurevessel 20 and the pump cylinder 10.

Supply of oil by the pump at constant pressure is from the annular space18 the oil passing through the delivery port 44 to the outlet line 46.

If the feed rate of pressurised oil from the pump cylinder 10 into theannular space 18 and the interspace 28 is in excess of supplyrequirements during the pressurising stroke of the ram 35 the excess oilpasses into the accumulator space 34. In order to accommodate this flowof high pressure oil into the accumulator space 34 the outer highpressure vessel 20 together with the low pressure cylinder 6 movesvertically upwards, guided by the pillars 22. The pressure of oil in thelow pressure cylinder 6 provides a reaction to the load exerted by thehigh pressure oil in the accumulator space 34 on the annular plug 32.The upward movement of the pressure vessel 20 and the cylinder 6increases the volume of the accumulator space 34 to accommodate theexcess oil and maintains a constant oil delivery pressure in thedelivery port 44 during the compression stroke of the ram 35. During theinduction stroke of the ram 35 the oil delivery pressure in the deliveryport 44 is maintained constant by the downward movement of the cojoinedpressure vessel 20 and cylinder 6, forcing high pressure oil to flow outof the accumulator space 34 down the annular space 28 into the deliveryport 44. Thus a feed of high pressure oil is supplied by the pump at aconstant required rate both during the induction and pressurisingstrokes of the ram 35.

The pressure of the oil in the accumulator space 34 acting on theexternal shoulder 48 of the pump cylinder 10 applies a downwards loadingon the pump cylinder 10 so that the flat seating 14 in the counterbore12 of the pump cylinder 10 is pressed against the upper end face of thevalve member 13 on the pump base 2.

The contact pressure exerted between the seating 14 of the counterbore12 and the upper end face 15 of the valve member 13 controls thepressure at which oil bleeds from the bore 11 of the pump cylinder 10.This contact pressure is dependent on the area of the external shoulder48 of the pump cylinder 10 relative to the area of the base 14 in thecounterbore 12 of the pump cylinder 10.

FIG. 2 shows one use of the pump in supplying high pressure oil tohydrostatic extrusion equipment which comprises a long bore extrusionchamber 49 fitted with an extrusion die 50. A billet 51 of large lengthto diameter ratio is extruded through the die 50 by pressurisation ofoil surrounding the billet 51 in the bore of the chamber 49. Highpressure oil is supplied to the bore of the chamber 49 from a pump 52 ofthe kind described above, the high pressure oil outlet line 46 of thepump being connected with an oil inlet port 53 at the rear end of theextrusion chamber 49. Low pressure oil is supplied to the pump throughthe low pressure oil feed line 54 from a low pressure oil supply system55.

Connected into the low pressure oil feed line 54 is a low pressure oilaccumulator 56, which allows a fiow of low pressure oil into and out ofthe oil inlet port 37 and the low pressure cylinder 6 of the pump inaccordance with the vertical movement of the outer pressure vessel andthe low pressure cylinder 6 of the pump thus maintaining a constantpressure supply of low pressure oil in the oil inlet port 37. The lowpressure oil supply system 55 comprises an oil tank, a low pressure pumpdriven by an electric motor together with means for cooling andfiltering the oil. Oil leakage from the die 50 of the extrusion chamber49 is returned to the low pressure oil supply system 55 from an oilleakage tank 57 by means of a pump 58 and an oil return pipe 59.

In the construction shown in FIG. 1 of the drawings the pump cylinder 10is acted On by oil pressure on both its inner and outer surfaces. Theouter surface of the pump cylinder 10 is supported by the highpressureoil in the annular interspace 28. The inner surface, however, issubjected to the oil pressures acting in the bore 11 and undergoes acyclic variation from the low pressure of the oil entering the bore 11from the oil inlet port 37 to the high pressure required to cause theoil to bleed from the bore 11 of the pump cylinder 10, this pressureexceeding the delivery pressure by a small amount.

With this type of pressure loading the pump cylinder 10 is subjected tocompressive cyclic strains. Whilst it is known that this type of strainvariation does induce fatigue failure, experiment has shown that thefatigue life is greater than when the pump cylinder is subjected to atensile cyclic strain variation. The outer pressure vessel 20 however,is not fatigued as the pressure in the annular interspace 28 isconstant. However in applications where the supply pressure variesaccording to the requirements of the process being supplied, the outerpressure vessel 20 is still only fatigued by one strain cycle in eachperformance of the process.

We claim:

1. A high pressure fluid pump having a cylinder contained by a pressurevessel, a reciprocable plunger for pressurising fluid in the cylinder,an interspace being defined between the cylinder and the pressurevessel, means being provided for controlled feeding of pressurized fluidfrom the pump cylinder into the interspace, means for supplying at aconstant rate pressurized fluid at constant pressure from theinterspace, the interspace defined between the pump cylinder and thepressure vessel being of variable volume to accomodate for differencesbetween the rate of feeding of fluid from the pump cylinder into theinterspace and the rate of supply of pressurized fluid from theinterspace to thereby provide said constant rate supply.

2. A high pressure fluid pump as claimed in claim 1 wherein a separatefluid accumulator space of variable volume is provided in connectionwith the interspace defined between the pump cylinder and the pressurevessel to accommodate for differences between the rate of feeding offluid from the pump cylinder into the interspace and the rate of supplyof pressurised fluid from the interspace.

3. A high pressure fluid pump as claimed in claim 2 wherein the fluidaccumulator space is an extension of the interspace defined between thepump cylinder and the pressure vessel, variation of the volume of thefluid accumulator space being obtained by longitudinal movement of thepump cylinder and the pressure vessel relative to each other.

4. A high pressure fluid pump as claimed in claim 2 wherein the pumpcylinder has an axial extension of smaller cross section than the mainbody of the pump cylinder the axial extension of the pump cylinder beingsealed in passage through the wall of the pressure vessel and the fluidaccumulator space of variable volume being defined between the axialextension of the pump cylinder and the pressure vessel, variation of thevolume of the fluid accumulator space being obtained by longitudinalmovement of the pump cylinder and the pressure vessel relative to eachother.

5. A high pressure fluid pump as claimed in claim 1 wherein the meansfor controlled feeding of pressurised fluid from the pump cylinder intothe interspace between the pump cylinder and the pressure vessel is anonreturn valve.

6. A high pressure fluid pump as claimed in claim 1 wherein the meansfor controlled feeding of pressurised fluid from the pump cylinder intothe interspace between the pump cylinder and the pressure vesselcomprises a valve seating around one end of the bore of the pumpcylinder, the valve seating bearing against a valve member at the end ofthe pump cylinder, means being provided for establishing a pressurebetween the valve seating and the valve member to control the pressureat which fluid feeds between the valve seating and the valve member fromthe pump cylinder into the interspace.

' 7. A high pressure fluid pump as claimed in claim 6 wherein the pumpcylinder has an axial extension of smaller cross section than the mainbody of the pump cylinder the axial extension of the pump cylinder beingsealed in passage through the wall of the pressure vessel, a fluidaccumulator space being thus defined between the axial extension of thepump cylinder and the pressure vessel, the pressure vessel beinglongitudinally movable relative to the pump cylinder whereby the fluidaccumulator space is of variable volume to accommodate for differencesbetween the rate of feeding of fluid from the pump cylinder into theinterspace and the rate of supply of pressurised fluid from theinterspace, means being provided for loading the pressure vessellongitudinally to maintain the pressure of the fluid in the accumulatorspace and in the interspace between the pump cylinder and the pressurevessel, the pressure of the fluid in the accumulator space acting on ashoulder between the axial extension of the pump cylinder and the mainbody of the pump cylinder to apply a longitudinal loading on the pumpcylinder which establishes the pressure between the valve seating andthe valve member to control the pressure at which fluid feeds from thepump cylinder into the interspace.

8. A high pressure fluid pump as claimed in claim 7 wherein a plunger isprovided in the bore of the pump cylinder for induction of fluid intoand pressurisation of fluid in the pump cylinder, the means for loadingthe pressure vessel longitudinally to maintain the pressure of fluid inthe accumulator space and in the interspace between the pump cylinderand the pressure vessel comprising a low pressure piston and cylinderarrangement acting on the pressure vessel, the cylinder of the pistonand cylinder arrangement having a connection with the bore of the pumpcylinder through a nonreturn valve for feed of low pressure fluid intothe pump cylinder on the induction stroke of the plunger in the pumpcylinder.

References Cited UNITED STATES PATENTS 2,891,564 6/1959 Jeromson, Jr.103-223X 3,005,412 10/1961 Camp 103223X 3,027,848 4/1962 Merkle 103223X3,128,941 4/1964 Waibel 103-153X ROBERT M. WALKER, Primary Examiner

